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  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      /*  let i = confirm("输入没姓名");
      console.log(i); //true
      var s1 = "100";
      console.log(s1); //100
      console.log(typeof s1); //string
      console.log("====================");
      var res = s1 - 0;
      console.log(res); //100
      console.log(typeof res); //number
       */
      // 2. toString
      //   var n = null;
      //   console.log(n);
      //   console.log(typeof n);
      //   console.log("-------------------------");
      //   var res = String(n);
      //   console.log(res);
      //   console.log(typeof res);
      //   console.log(false + 100);
      //   console.log(100 + "435"); // "100435"
      //   console.log(typeof (100 + "435"));
      //   var a, b;
      //   console.log(a == b);
      //   console.log(Boolean(null));
      console.log(NaN == NaN);
    </script>
  </body>
</html>
